The interesting thing about 12V car systems is that most use 5-6 volts at the dashboard. Chrysler products usually use a voltage limiter or reducer mounted behind the gauges.
Mopar gauges operate by current heating an element in the gauge. they are relatively insensitive to voltage spikes. As a result, the voltage limiter acts like a mechanical pulse-width-modulation unit.

You can achieve the same result but with regulated 5 volt output by building a voltage reducer using commonly available PC power supply chips. There are many articles on this build on the Web.

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